U.S. patent number 6,064,859 [Application Number 08/743,121] was granted by the patent office on 2000-05-16 for transmit and receive payload pair and method for use in communication systems.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Raymond J. Leopold, Keith A. Olds, Peter A. Swan.
United States Patent |
6,064,859 |
Leopold , et al. |
May 16, 2000 |
Transmit and receive payload pair and method for use in
communication systems
Abstract
Transmit, receive, and processing functions of a communication
satellite are performed by two communication payload satellites. A
transmit payload satellite (20) and a receive payload satellite
(10) communicate via a crosslink (30,28) which provides the
communication path between the two parts of the transmit and
receive payload pair (50). The receive payload satellite (10) is
optimized to perform substantially all of the receiving and
processing functions required in space. The transmit payload
satellite (20) is optimized to perform substantially all of the
transmitting functions. The optimization process takes into account
the location in space for the two separate payloads, where
trade-offs are made with respect to electromagnetic signal
interference issues, size, weight, power, and complexity.
Inventors: |
Leopold; Raymond J. (Tempe,
AZ), Swan; Peter A. (Paradise Valley, AZ), Olds; Keith
A. (Mesa, AZ) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
24987596 |
Appl.
No.: |
08/743,121 |
Filed: |
November 4, 1996 |
Current U.S.
Class: |
455/13.1;
455/427 |
Current CPC
Class: |
H04B
7/18515 (20130101); H04B 7/18521 (20130101) |
Current International
Class: |
H04B
7/185 (20060101); H04B 007/185 (); H04Q
007/20 () |
Field of
Search: |
;455/427,430,11.1,12.1,13.1,13.3,16 ;370/316 ;244/158R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Vo; Nguyen
Attorney, Agent or Firm: Whitney; Sherry J. Klekotka; James
E.
Claims
What is claimed is:
1. In a satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, a method of providing said
communication services comprising the steps of:
configuring a first number of receive payload satellites having at
least one antenna optimized to operate in a receive-only mode at
first locations in orbits around the earth;
configuring a second number of transmit payload satellites having
at least one antenna optimized to operate in a transmit-only mode
at second locations in orbits around the earth, wherein said first
locations and said second locations being chosen to separate high
power transmitter operations associated with said transmit payload
satellites from sensitive receive operations associated with said
receive payload satellites;
positioning said first number of receive payload satellites at said
first locations in orbits around the earth, wherein said first
number of receive payload satellites are adapted to perform
substantially only receiving functions and substantially none of
the transmitting functions for uplink communication channels from
said plurality of communication units, transmitting functions for
short crosslink communication channels, receiving functions for
long crosslink communication channels, and a first set of
space-based processing functions;
establishing at least one uplink communication channel between a
first receive payload satellite and a first communication unit;
positioning said second number of transmit payload satellites at
said second locations in orbits around the earth, wherein said
second number of transmit payload satellites are adapted to perform
substantially only
transmitting functions and substantially none of the receiving
functions for downlink communication channels to said plurality of
communication units, receiving functions for short crosslink
communication channels, transmitting functions for long crosslink
communication channels, and a second set of space-based processing
functions;
establishing a first short crosslink from said first receive
payload satellite to a first transmit payload satellite, said first
short crosslink providing at least one short crosslink
communication channel for passing data between said first transmit
payload satellite and said first receive payload satellite, thereby
forming a first transmit and receive payload pair;
establishing a second short crosslink from a second receive payload
satellite to a second transmit payload satellite, said second short
crosslink providing at least one short crosslink communication
channel for passing data between said second transmit payload
satellite and said second receive payload satellite, thereby
forming a second transmit and receive payload pair;
establishing at least one downlink communication channel between
said second transmit payload satellite and a second communication
unit; and
establishing at least one long crosslink communication channel
between said first transmit payload satellite and said second
receive payload satellite, thereby coupling said first transmit and
receive payload pair to said second transmit and receive payload
pair so that communication service data sent from said first
communication unit is received by said second communication unit,
wherein said communication service data is sent over said at least
one uplink communication channel, said first short crosslink, said
at least one long crosslink communication channel, said second
short crosslink, and said at least one downlink communication
channel.
2. The method of providing communication services as claimed in
claim 1 wherein said first locations and said second locations are
in geosynchronous orbits around the earth.
3. The method of providing communication services as claimed in
claim 1 wherein said first locations and said second locations are
in non-geosynchronous orbits around the earth.
4. The method of providing communication services as claimed in
claim 1 wherein said first locations are in geosynchronous orbits
around the earth and said second locations are in
non-geosynchronous orbits around the earth.
5. The method of providing communication services as claimed in
claim 1 wherein said first locations are in non-geosynchronous
orbits around the earth and said second locations are in
geosynchronous orbits around the earth.
6. The method of providing communication services as claimed in
claim 1 wherein said establishing a first short crosslink step
comprises the step of:
providing said first short crosslink using at least one
electromagnetic signal means.
7. The method of providing communication services as claimed in
claim 1 wherein said establishing a first short crosslink step
comprises the step of:
providing said first short crosslink using at least one laser
signal means.
8. The method of providing communication services as claimed in
claim 1 wherein said establishing a second short crosslink step
comprises the step of:
providing said second short crosslink using at least one
electromagnetic signal means.
9. The method of providing communication services as claimed in
claim 1 wherein said establishing a second short crosslink step
comprises the step of:
providing said second short crosslink using at least one laser
signal means.
10. The method of providing communication services as claimed in
claim 1 wherein said establishing at least one long crosslink
communication channel step comprises the step of:
providing said at least one long crosslink communication channel
using at least one electromagnetic signal means.
11. The method of providing communication services as claimed in
claim 1 wherein said establishing at least one long crosslink
communication channel step comprises the step of:
providing said at least one long crosslink communication channel
using at least one laser signal means.
12. The method of providing communication services as claimed in
claim 1 further comprising the steps of:
providing at least one command link between said first transmit and
receive payload pair and at least one system control center;
and
providing at least one telemetry link between said first transmit
and receive payload pair and said at least one system control
center.
13. The method of providing communication services as claimed in
claim 1 further comprising the steps of:
providing at least one command link between said second transmit
and receive payload pair and at least one system control center;
and
providing at least one telemetry link between said second transmit
and receive payload pair and said at least one system control
center.
14. In a satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, a method of operating a receive
payload satellite in a transmit and receive payload pair, said
method comprising the steps of:
configuring said receive payload satellite to perform substantially
all of the uplink receiving and processing functions and
substantially none of the associated downlink transmitting
functions;
positioning said receive payload satellite in a first location in
orbit around the earth wherein said first location is chosen to
separate high power transmitter operations associated with at least
one transmit payload satellite at a second location in orbit from
sensitive receive operations associated with said receive payload
satellite;
receiving uplink received signals from at least one of said
plurality of communication units;
converting said uplink received signals into uplink received
data;
receiving crosslink received signals from at least one transmit
payload satellite in another transmit and receive payload pair,
said transmit and receive payload pair being coupled to said
another transmit and receive payload pair using a long
crosslink;
converting said crosslink received signals into crosslink received
data;
processing said uplink received data and crosslink received data
into payload data and crosslink transmitted data;
converting said crosslink transmitted data into crosslink
transmitted signals;
sending said crosslink transmitted signals to a transmit payload
satellite via a short crosslink, said short crosslink coupling said
transmit payload satellite to said receive payload satellite,
thereby forming said transmit and receive payload pair; and
using some of said payload data to control said receive payload
satellite.
15. The method of operating a receive payload satellite as claimed
in claim 14, further comprising the steps of:
receiving uplink command signals from at least one system control
center;
converting said uplink command signals into uplink command data;
and
processing said uplink command data into said payload data and said
crosslink transmitted data.
16. In a satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, a method of operating a transmit
payload satellite in a transmit and receive payload pair, said
method comprising the steps of:
configuring said transmit payload satellite to perform
substantially all of the downlink transmitting functions and
substantially none of the associated uplink receiving
functions;
positioning said transmit payload satellite in a second location in
orbit around the earth, wherein said second location is chosen to
separate high power transmitter operations associated with said
transmit payload satellite at said second location from sensitive
receive operations associated with at least one receive payload
satellite at a first location in orbit around the earth;
establishing a short crosslink to a receive payload satellite, said
short crosslink coupling said transmit payload satellite to said
receive payload satellite to form said transmit and receive payload
pair;
receiving crosslink received signals from said receive payload
satellite via said short crosslink;
converting said crosslink received signals into crosslink received
data;
using said crosslink received data to determine payload data,
crosslink transmitted data, and downlink transmitted data;
using said payload data to control said transmit payload
satellite;
converting said crosslink transmitted data into crosslink
transmitted signals;
establishing a long crosslink to a receive payload satellite in a
different orbital plane, said long crosslink coupling said transmit
payload satellite in said transmit and receive payload pair to said
receive payload satellite which is in another transmit and receive
payload pair;
transmitting said crosslink transmitted signals to said receive
payload satellite in said another transmit and receive payload pair
via said long crosslink;
converting said downlink transmitted data into downlink transmitted
signals; and
transmitting said downlink transmitted signals to at least one of
said plurality of communication units.
17. The method of operating a transmit payload satellite as claimed
in claim 16, further comprising the steps of:
using said crosslink received data to determine downlink telemetry
data;
converting said downlink telemetry data into downlink telemetry
signals; and
transmitting said downlink telemetry signals to at least one system
control center.
18. A satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, a transmit and receive payload
pair comprising:
a receive payload satellite comprising means for receiving signals
via uplink communication channels from said plurality of
communication units, said means for receiving including an uplink
antenna that has been optimized to operate in a receive-only mode
when said receive payload satellite is positioned in a first orbit
around the earth, means for transmitting signals via short
crosslink communication channels to a transmit payload satellite in
said transmit and receive payload pair, means for receiving signals
via long crosslink communication channels from a second transmit
payload satellite in a second transmit and receive payload pair,
and means for performing a first set of space-based processing
functions required to provide said communication services, said
first set comprising on-board processing functions for said receive
payload satellite and substantially all processing functions for
said transmit payload satellite in said transmit and receive
payload pair; and
a transmit payload satellite comprising means for transmitting
signals via downlink communication channels to said plurality of
communication units, said means for transmitting including a
downlink antenna that has been optimized to operate in a
transmit-only mode when said transmit payload satellite is
positioned in a second orbit around the earth, means for receiving
signals via short crosslink communication channels from a receive
payload satellite in a transmit and receive payload pair, means for
transmitting signals via long crosslink communication channels to
another receive payload satellite in another transmit and receive
payload pair, and means for performing a second set of space-based
processing functions required to provide said communication
services, wherein said first orbit and said second orbit are chosen
to physically separate high power transmitter operations associated
with said transmit payload satellite from sensitive receive
operations associated with said receive payload satellite.
19. The satellite communication system as claimed in claim 18
wherein said receive payload satellites further comprise:
means for converting uplink received signals from at least one of
said plurality of communication units into uplink received
data;
means for converting crosslink transmitted data into crosslink
transmitted signals;
means for converting crosslink received signals which are received
on at least one long crosslink communication channel into crosslink
received data; and
a processing unit for processing said uplink received data, said
crosslink received data, payload data, and said crosslink
transmitted data.
20. The satellite communication system as claimed in claim 18,
wherein said transmit payload satellites further comprise:
means for converting downlink transmitted data into downlink
transmitted signals.
21. The satellite communication system as claimed in claim 18
further comprising:
a system control center with a command channel to at least one
receive payload satellite in one of said plurality of transmit and
receive payload pairs and with a telemetry channel from at least
one transmit payload satellite in a second one of said plurality of
transmit and receive payload pairs for controlling operations of
said satellite communication system.
22. In a satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, wherein a transmit and receive
payload pair comprises a receive payload satellite and a transmit
payload satellite that are coupled to each other using a short
crosslink communication channel, said receive payload satellite
comprising:
an uplink antenna for receiving uplink received signals from at
least one of said plurality of communication units, said uplink
antenna being optimized to operate in a receive-only mode at a
first location in orbit around the earth, wherein said first
location is chosen to separate high
power transmitter operations associated with at least one transmit
payload satellite at a second location in orbit from sensitive
receive operations associated with said receive payload
satellite;
an uplink receiver unit coupled to said uplink antenna for
converting said uplink received signals from at least one of said
plurality of communication units into uplink received data;
performs substantially all space-based receiving functions that are
required to provide said communication services said uplink
receiver unit being optimized to operate at said first
location;
a crosslink antenna unit for providing said short crosslink
communication channel between said receive payload satellite and
said transmit payload satellite in said transmit and receive
payload pair, said transmit payload satellite being in a second
location in orbit around the earth and for providing at least one
long crosslink communication channel between said receive payload
satellite and at least one other transmit payload satellite in
another transmit and receive payload pair;
a crosslink receiver unit coupled to said crosslink antenna unit
for converting crosslink received signals into crosslink received
data;
a crosslink transmitter unit coupled to said crosslink antenna unit
for converting crosslink transmitted data into crosslink
transmitted signals; and
a processing unit coupled to said uplink receiver unit, to said
crosslink receiver unit, and to said crosslink transmitter unit for
processing said uplink received data, said crosslink received data,
said crosslink transmitted data, and payload data, said processing
unit providing all on-board processing functions for said receive
payload satellite and substantially all processing functions for
said transmit payload satellite in said transmit and receive
payload pair.
23. In a satellite communication system which uses a plurality of
transmit and receive payload pairs, which are coupled to each other
via long crosslinks, to provide communication services to a
plurality of communication units, wherein a transmit and receive
payload pair comprises a receive payload satellite and a transmit
payload satellite that are coupled to each other using a short
crosslink communication channel, said transmit payload satellite
comprising:
a downlink antenna for transmitting downlink transmitted signals to
at least one of said plurality of communication units, said
downlink antenna being optimized to operate in a transmit-only mode
at a second location in orbit around the earth, wherein said second
location is chosen to separate high power transmitter operations
associated with said transmit payload satellite at said second
location from sensitive receive operations associated with at least
one receive payload satellite at a first location in orbit around
the earth;
a downlink transmitter unit coupled to said downlink antenna for
converting downlink transmitted data into said downlink transmitted
signals, said downlink transmitter unit performing substantially
all associated space-based transmitting functions that are required
to provide said communication services and substantially none of
space-based receiving functions that are required to provide said
communication services;
a crosslink receiver unit coupled to said downlink transmitter unit
for converting crosslink received signals into crosslink received
data, wherein said crosslink received signals are received on said
short crosslink communication channel from said receive payload
satellite of said transmit and receive payload pair, said crosslink
received data comprising instructional data from said receive
payload satellite which said transmit payload satellite uses to
modify its operations;
a crosslink transmitter unit coupled to said crosslink receiver
unit for converting crosslink transmitted data into crosslink
transmitted signals which are transmitted on at least one long
crosslink communication channel between said transmit payload
satellite and at least one other receive payload satellite in
another transmit and receive payload pair; and
a crosslink antenna unit coupled to said crosslink receiver unit
for providing said short crosslink communication channel and to
said crosslink transmitter unit for providing said at least one
long crosslink communication channel.
Description
FIELD OF THE INVENTION
The present invention pertains to communication systems and, more
particularly, to an apparatus and methods for transmitting signals
to and receiving signals from payloads in communication
systems.
BACKGROUND OF THE INVENTION
Satellites have the ability to provide line-of-sight communication
paths to large geographical areas. Because of this, many different
systems have been designed and are in various stages of
development. These satellite based systems will provide
communication and data services to a large number of mobile,
portable and fixed subscriber equipment in many places around the
world where users cannot presently be economically serviced by
terrestrial based systems.
Modern satellite communication systems tend to use more than one
satellite to fulfill their mission. Multiple satellites provide
increased capacity, coverage and flexibility for the system. This
multiplicity of satellites has led to the extensive use of
inter-satellite links to provide system control and coordination.
These relatively new factors in satellite systems provide
opportunities to optimize the design of the satellites outside the
traditional boundaries.
In the design of satellite communication systems, one of the
concerns for system designers is the link performance. In general
terms, the forward or reverse link performance is directly related
to the power transmitted from the earth station or the satellite,
the gains of the receiving antennas, path losses, and interference
levels. Link gains which affect the satellite's configuration are
provided by the on-board amplification and antennas. The
transmitted power is a major design concern because it affects the
mass and the primary power requirements of the satellite. Antenna
size and configuration are also important considerations.
Other satellite considerations include transmitter duty cycle,
modulation efficiency, power supply system conversion efficiency,
heat dissipation, and temperature control. In general, any changes
in these factors cause changes in the power output capability and
usually correspond to an increase in the payload weight.
Satellites also have some form of thermal control to manage the
temperature extremes. In a satellite, the temperature is controlled
by balancing the amounts of radiated and absorbed energy. Internal
inefficiencies in the components can generate heat, along with
chemical reactions. External sources such as the sun also
contribute to the heating of the satellite. Heat loss can be
controlled by managing the emissivity of the satellite's
surfaces.
The satellite system is a collection of multiple stage subsystems.
In a most general view, the satellite system can be subdivided into
a receive subsystem, a transmit subsystem, and a processing
subsystem. What are needed are a method and apparatus which ensure
more on-orbit capability by optimizing the hardware complexity,
weight, power, and launch costs.
Interference is also a problem which must be dealt with by the
satellite system designers. Interference can be due to other
space-based transmitters or terrestrial-based transmitters.
Interference can also be due to on-board sources. Therefore, what
are also needed are a method and apparatus for minimizing
interference problems.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention can be
derived by referring to the detailed description and claims when
considered in connection with the figures, wherein like reference
numbers refer to similar items throughout the figures, and:
FIG. 1 shows a block diagram of a satellite communication system in
which the space based communication facilities are provided by a
transmit and receive payload pair in accordance with a preferred
embodiment of the present invention;
FIG. 2 shows a block diagram for a receive payload satellite in a
transmit and receive payload pair in accordance with a preferred
embodiment of the present invention;
FIG. 3 shows a block diagram for a transmit payload satellite in a
transmit and receive payload pair in accordance with a preferred
embodiment of the present invention;
FIG. 4 shows a flow chart for a method for using a receive payload
satellite in a transmit and receive payload pair in accordance with
a preferred embodiment of the present invention; and
FIG. 5 shows a flow chart for a method for using a transmit payload
satellite in a transmit and receive payload pair in accordance with
a preferred embodiment of the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The present invention describes a transmit and receive payload pair
in which the transceiver portion of the communication satellite is
separated into two satellite payloads, one for the transmit
function and one for the receive and processing functions. The
combination of a transmit payload satellite and a receive payload
satellite is referred to herein as a "transmit and receive payload
pair". The concept of transmit and receive payload pair, one for
transmit and one for receive, allows system designers tremendous
flexibility on size, weight, power, and complexity. The key is that
complexity issues of receive and payload processing are physically
separated from the thermal issues due to power dissipated during
the associated transmitting of the communications signals. This
optimization for thermal and payload complexity leads to tremendous
savings in system level trades across the mission requirements to
provide communication services.
FIG. 1 shows a block diagram of a satellite communication system
100 in which the space based communication facilities are provided
by a transmit and receive payload pair 50 in accordance with a
preferred embodiment of the present invention. As shown in FIG. 1,
satellite communication system 100 contains multiple transmit and
receive payload pairs 50. Long crosslink communication channels
between different transmit and receive payload pairs 50 are
provided by long crosslinks 28. A long crosslink communication
channel 28 is a unidirectional path from a first crosslink device
on a transmit payload satellite to a second crosslink device on a
receive payload satellite. When transmitting and receiving
communication units 14 are not serviced by the same payload pair
50, a uni-directional data path from a transmit payload satellite
20 in one transmit and receive payload pair 50 to a receive payload
satellite 20 in another transmit and receive payload pair 50 is
sufficient to provide communication services from one communication
unit 14 to another communication unit 14. The long crosslink
communication channel 28 can be provided by electromagnetic
signal means or laser signal means. Additional data sent on long
crosslink 28 is used to control and coordinate the operation of
receive satellite 10 and transmit satellite 20. Long crosslink 28
is primarily used to transfer received communication service data
from one transmit and receive payload pair 50 to another transmit
and receive payload pair 50 so that the communication service data
can be transmitted from one communication unit 14 to another
communication unit 14.
At least one uplink communication channel is provided via uplink 12
from communication units 14 that are located proximate to the
surface of the earth 35 to an uplink device on receive payload
satellite 10. An uplink communication channel is provided by
electromagnetic signal means or laser signal means. In FIG. 1, only
two communication units 14 and only two uplinks 12 are shown to
simplify the explanation of the preferred embodiment shown. Those
skilled in the art will recognize that any number of communication
units 14 and uplinks 12 are possible.
At least one downlink communication channel is provided via
downlink 18 from a downlink device on transmit payload satellite 20
to communication units 14 that are located proximate to the surface
of the earth 35. A downlink communication channel is provided by
electromagnetic signal means or laser signal means. In FIG. 1, only
two communication units 14 and only two downlinks 18 are shown to
simplify the explanation of the preferred embodiment shown. Those
skilled in the art will recognize that any number of communication
units 14 and downlinks 18 are possible.
Those skilled in the art will also recognize that a communication
unit in a communication system may, from time to time, perform
functions of both a transmitting device and a receiving device or
change from a transmitting device to a receiving device and vice
versa. These changes are usually controlled by a processor. A
communication unit can be, for example, a hand-held, portable
cellular telephone adapted to transmit data to and/or receive data
from transmit and receive payload pair 50. A communication unit can
also be a facsimile device, pager, data terminal, or any other type
of communication device.
A communication unit 14, which has been adapted to operate with
said transmit and receive payload pair 50, comprises a transmitting
device for transmitting uplink signals on at least one uplink
communication channel 24 to at least one transmit and receive
payload pair 50, a receiving device for receiving downlink signals
on at least one downlink communication channel 18 from at least one
transmit and receive payload pair 50, and a processor which is
coupled to both the transmitting device and the receiving device
and which is used for controlling the transmitting device, the
receiving device and the communication unit 14.
Receive payload satellite 10 also has a communication channel with
transmit payload satellite 20 via short crosslink 30. Short
crosslink 30 provides at least one short crosslink communication
channel for passing data between the two parts of transmit and
receive payload pair 50. A short crosslink communication channel 30
is primarily a unidirectional path from a first crosslink device on
a receive payload satellite 10 to a second crosslink device on a
transmit payload satellite 20. In some embodiments, however, data
can be sent in the reverse direction for various purposes such as
maintaining communications, link synchronization, error control and
recovery, or the like. A unidirectional data path from receive
payload satellite 10 to transmit payload satellite 20 is sufficient
to provide communication services from one communication unit 14 to
another communication unit 14. The short crosslink communication
channel 30 is provided by electromagnetic signal means, a
signal-carrying cable means, or laser signal means. Additional data
sent on short crosslink 30 is used to control and coordinate the
operation of receive satellite 10 and transmit satellite 20. Short
crosslink 30 is primarily used to transfer received communication
service data from receive payload satellite 10 to transmit payload
satellite 20 so that the communication service data may be
transmitted to communication unit 14.
In a preferred embodiment of the present invention, the two payload
satellites in transmit and receive payload pair 50 fly in the same
orbital plane 40 with a small orbital phase difference that has a
lead/follow orientation with a short distance between the payload
satellites. In another embodiment, the two payload satellites in
transmit and receive payload pair 50 are in separated orbital
planes with the same or different angle of inclination. In other
embodiments, receive payload satellite 10 and transmit payload
satellite 20 are widely separated; however, constant line of sight
is necessary for crosslinking.
Referring again to FIG. 1, a command channel is established via
command link 24 from system control center 22 to receive payload
satellite 10, and a telemetry channel is established via telemetry
link 26 from transmit payload satellite 20 to system control center
22. System control center 22 controls operation of satellite
communication system 100 and provides telemetry, tracking and
control (TT&C) signals for transmit and receive payload pair
50. Telemetry, tracking and control signals are key service
features which should be provided to each satellite. The telemetry
function is desirable to provide a way to monitor and evaluate the
satellites' performance. The command function is desirable to
provide a way to control satellite operation. The tracking function
is desirable to perform orbit corrections.
In a preferred embodiment such as shown in FIG. 1, with respect to
system control center 22, unidirectional links are shown in a
direction toward receive payload satellite 10 and from transmit
payload satellite 20. A uni-directional link is also shown for
short crosslink 30. Short crosslink 30 provides the necessary
transmission path for the communication service data and the
telemetry, tracking and control signals between the two payloads.
For example, TT&C signals can be transmitted via command link
24 to receive payload satellite 10, between receive payload
satellite 10 and transmit payload satellite 20 via short crosslink
30, and can be retransmitted to earth 35 from transmit payload
satellite 20 via telemetry link 26. In addition, some TT&C
signals can be transmitted from transmit payload satellite 20 to
receive payload satellite 10 by using telemetry link 26, system
control center 22, and command link 24. In an alternate embodiment,
transmit payload satellite 20 can send information directly to
receive payload satellite 10.
FIG. 2 shows a block diagram for a receive payload satellite 10
(FIG. 1) in a transmit and receive payload pair 50 (FIG. 1) in
accordance with a preferred embodiment of the present invention.
Uplink antenna 202 is used to receive signals from communication
units 14 (FIG. 1) and from system control center 22 (FIG. 1). It
will be understood that while each receive payload satellite 10 is
illustrated in FIG. 2 as having a single uplink antenna 202, each
uplink antenna 202 will typically comprise several antennas, so
that receive payload satellite 10 can communicate with more than
one communication unit at a time and with system control center 22
(FIG. 1). Those skilled in the art will appreciate that instead of
a bank of discrete, uni-directional antennas, uplink antenna 202
can be implemented as a single, phased-array antenna or a
combination of unidirectional antennas and phased-array antennas.
In a preferred embodiment, uplink antenna 202 is an uplink device
for signal reception that has been optimized to operate in a
receive-only mode and when positioned in a particular earth orbit.
For example, the size of the antenna is more closely determined
because it only has to function in a receive mode in a
geosynchronous orbit.
Uplink antenna 202 is coupled to uplink receiver unit 204 which can
contain a low noise amplifier (LNA) and elements to control the
operation of uplink antenna 202. Uplink receiver unit 204 is used
to convert and demodulate the signals received from uplink antenna
202 to signals which can be sent to processing unit 206. In a
preferred embodiment, uplink receiver unit 204 performs
substantially all space-based receiving functions that are required
to provide said communication services. In a preferred embodiment,
uplink receiver unit 204, has been adapted to operate while
positioned in a particular earth orbit. For example, receiver
sensitivity could be affected by the distance between receive
payload satellite 10 and transmit payload satellite 20.
Processing unit 206 desirably performs all of the functions
required to process data that is transmitted to receive payload
satellite 10 (FIG. 1). Processing unit 206 is coupled to crosslink
unit 208. Also, processing unit 206 desirably performs all of the
functions required to provide data to crosslink unit 208 for
transmission to transmit payload satellite 20 (FIG. 1). Crosslink
unit 208 is coupled to crosslink antenna unit 210 and can contain
elements to control the operation of crosslink antenna unit 210.
Crosslink unit 208 can provide just transmitting elements, just
receiving elements, or elements to separate transmitted and
received signals. Crosslink unit 208 can be a crosslink transmitter
unit, a crosslink receiver unit or a crosslink transceiver
unit.
Crosslink antenna unit 210 is coupled to crosslink unit 208 and
provides the transmission means to transmit crosslink signals to
transmit payload satellite 20 (FIG. 1). It will be understood that
while receive payload satellite 10 illustrated in FIG. 2 has a
single crosslink antenna unit 210, each crosslink antenna unit 210
can comprise several antenna elements, so that receive payload
satellite 10 (FIG. 1) can communicate with more than one other
transmit payload satellite at a time. Those skilled in the art will
appreciate that instead of a bank of discrete, uni-directional
antennas, crosslink antenna unit 210 can be implemented as a single
multi-beam, phased-array antenna or a combination of
uni-directional and phased-array antennas.
In an alternate embodiment of the present invention, crosslink
antenna unit 210 could also provide the reception means to receive
crosslink signals from transmit payload satellite 20 (FIG. 1). In
an alternate embodiment, crosslink unit 208 could be used to
convert the crosslink received signals into crosslink received data
which is processed by processing unit 206. As an example, this
crosslink received data could be used for synchronization and
TT&C functions.
Processing unit 206 provides control signals to uplink antenna 202,
uplink receiver unit 204, crosslink unit 208, and crosslink antenna
unit 210. Processing unit 206 receives status signals from uplink
antenna 202, uplink receiver unit 204, crosslink unit 208, and
crosslink antenna unit 210. Processing unit 206 provides all of the
on-board processing functions for receive payload satellite 10 and
substantially all of the processing functions for transmit payload
satellite 20. These functions can include but are not limited to
modulation, demodulation, decoding, switching, timing, storing,
coding, controlling and processing. Although only one processing
unit 206 is shown in FIG. 2, multiple processing units could be
used to perform these functions.
FIG. 3 shows a block diagram for a transmit payload satellite 20 in
transmit and receive payload pair 50 (FIG. 1) in accordance with a
preferred embodiment of the present invention. Downlink antenna 302
is used to transmit signals to communication units 14 (FIG. 1) and
to system control center 22 (FIG. 1). It will be understood that
while transmit payload satellite 20 illustrated in FIG. 3 has a
single downlink antenna 302, each downlink antenna 302 will
typically comprise several antennas, so that transmit payload
satellite 20 can communicate with more than one communication unit
14 (FIG. 1) at a time and with system control center 22 (FIG. 1).
Those skilled in the art will appreciate that instead of a bank of
discrete, uni-directional antennas, downlink antenna 302 can be
implemented as a single, phased-array antenna or a combination of
uni-directional antennas and phased-array antennas. In a preferred
embodiment, downlink antenna 302 is a downlink device for signal
distribution that has been optimized to operate in a transmit-only
mode and positioned in a particular earth orbit. For example, the
size of the antenna is more closely determined because it only has
to function in a transmit mode in non-geosynchronous orbits.
Downlink antenna 302 is coupled to downlink transmitter unit 304
which can contain a high power amplifier and elements to control
the operation of downlink antenna 302 and the high power amplifier.
Downlink transmitter unit 304 is used to convert and remodulate
data signals received from crosslink unit 306 onto signals which
are sent to downlink antenna 302. Crosslink unit 306 performs all
of the functions required to process data that was transmitted from
receive payload satellite 10 (FIG. 1). Crosslink unit 306 can
provide just transmitting elements, just receiving elements, or
elements to separate transmitted and received signals. Crosslink
unit 306 can be a crosslink transmitter unit, a crosslink receiver
unit or a crosslink transceiver unit. Crosslink unit 306 is coupled
to crosslink antenna unit 308 and can contain elements to control
the operation of crosslink antenna unit 308.
Crosslink antenna unit 308 provides a reception means to receive
crosslink signals from receive payload satellite 10 (FIG. 1). It
will be understood that while transmit payload satellite 20
illustrated in FIG. 2 has a single crosslink antenna unit 308, each
crosslink antenna unit 308 will typically comprise several antenna
elements, so that transmit payload satellite 20 (FIG. 1) can
communicate with more than one other receive payload satellite at a
time. Those skilled in the art will appreciate that instead of a
bank of discrete, uni-directional antennas, crosslink antenna unit
308 can be implemented as a single phased-array antenna or a
combination of uni-directional and phased-array antennas.
Controller unit 320 is coupled to downlink transmitter unit 304 and
crosslink unit 306. Controller unit 320 provides control signals to
downlink antenna 302, downlink transmitter unit 304, crosslink unit
306, and crosslink antenna unit 308. Controller unit 320 obtains
status signals from downlink antenna 302, downlink transmitter unit
304, crosslink unit 306, and crosslink antenna unit 308.
FIG. 4 shows a flow chart for a method for using a receive payload
satellite in a transmit and receive payload pair in accordance with
a preferred embodiment of the present invention. Procedure 400
starts in step 402. In step 404, signals are received by receive
payload satellite 10 (FIG. 1). The received signals can originate
from many different sources including but not limited to
communication units. The frequency range for the received signals
can be from RF to light depending on the nature of the
communication system.
Some of the received signals are received on uplink 12 (FIG. 1)
from communication units 14 (FIG. 1) and these signals are
identified as uplink received signals. Some of the received signals
are received on long crosslink 28 (FIG. 1) from transmit payload
satellites 20 and these signals are identified as crosslink
received signals. Some of the received signals are received on
command link 24 from system control centers 22 and these signals
are identified as uplink command signals. In a preferred embodiment
of the present invention, the crosslink received signals originate
from transmit payload satellite 20 (FIG. 1) which is not associated
with this receive payload satellite 10 (FIG. 1) in the transmit and
receive payload pair 50 (FIG. 1). In alternate embodiments, the
crosslink received signals can originate from any one of a number
of other payloads.
In step 406, the received signals are converted to received data.
Conversion processes include but are not limited to frequency
conversion and demodulation. Received data packets are tagged with
their destination. This can be done by system control center 22
(FIG. 1) or communication unit 14 (FIG. 1), or a tag can be
attached by receive payload satellite 10 (FIG. 1). This tagging
operation associates a tag with the data packet based on which
channel, timeslot, frequency, code or other identifying means the
data packet is associated with.
The received data can be uplink received data, crosslink received
data, or uplink command data. The receiving device converts uplink
received signals into uplink received data, converts crosslink
received signals into crosslink received data, and converts uplink
command signals into uplink command data.
In step 408, the received data is processed into payload data and
crosslink transmitted data. The received data can contain but is
not limited to call processing data, user data, and payload data.
For example, call processing data can include data to begin a call,
data to maintain an on-going call,
and data to terminate a call. For example, user data can contain
voice, paging, facsimile or other similar data. Crosslink
transmitted data is data that is sent to transmit payload satellite
20 (FIG. 1). This data can contain but is not limited to data which
is used by transmit payload satellite 20 (FIG. 1) to operate and
data which is transmitted to communication units 14 (FIG. 1).
In step 410, the payload data is consumed by receive payload
satellite 10 (FIG. 1). Payload data can contain but is not limited
to control data, memory data, tracking data, program data, and call
processing data. As an example, portions of the payload data are
used to control the satellite's orientation in space. Other
portions of the payload data are used to control both the uplink
and crosslink antennas.
In step 412, the crosslink transmitted data packets are converted
to crosslink transmitted signals. Conversion processes can include
but are not limited to frequency conversion and modulation.
Crosslink transmitted data packets are tagged with their
destination. This is done by the communication unit or is attached
by receive payload satellite 10 (FIG. 1). This tagging operation
associates a tag with the data packet based on which channel,
timeslot, frequency, code or other identifying means the data
packet is associated with. The destination information is sent to
transmit payload satellite 20 (FIG. 1) with the data packet.
Transmit payload satellite 20 (FIG. 1) uses the destination
information to decide which channel is used to transmit the
downlink transmitted data.
In step 414, the crosslink transmitted signals are sent to transmit
payload satellite 20 (FIG. 1) over a short crosslink communication
channel 30 (FIG. 1) in a preferred embodiment. In an alternate
embodiment, data transmissions are accomplished over a tether
between receive payload satellite 10 (FIG. 1) and transmit payload
satellite 20 (FIG. 1). In this alternate embodiment, the crosslink
transmitted data packets would not have to be converted to
crosslink transmitted signals. Procedure 400 ends with step
416.
FIG. 5 shows a flow chart for a method for using a transmit payload
satellite in a transmit and receive payload pair in accordance with
a preferred embodiment of the present invention. Procedure 500
starts in step 502. In step 504, the crosslink transmitted signals
are received by transmit payload satellite 20 (FIG. 1) in transmit
and receive payload pair 50 (FIG. 1). In a preferred embodiment of
the present invention, the crosslink transmitted signals originate
from receive payload satellite 10 (FIG. 1) associated with this
transmit payload satellite 20 (FIG. 1) in the transmit and receive
payload pair 50 (FIG. 1). In alternate embodiments, the crosslink
transmitted signals can originate from any one of a number of other
payloads including but not limited to the receive payload satellite
associated with this transmit payload satellite in the transmit and
receive payload pair. In a preferred embodiment of the present
invention, the crosslink transmission means is an RF signal means.
In alternate embodiments, the frequency range for the crosslink
signals are from RF to light depending on the nature of the
communication system.
In step 506, the crosslink transmitted signals are converted to
crosslink received data. Conversion processes can include but are
not limited to frequency conversion and demodulation. Crosslink
received data packets are tagged with their destination. This
tagging operation associates a tag with the data packet based on
which channel, timeslot, frequency, code or other identifying means
the data packet is associated with.
In step 508, the crosslink received data is used to determine
payload data and downlink transmitted data. The crosslink received
data can contain but is not limited to call processing data, user
data, and payload data. For example, call processing data can
include data to begin a call, data to maintain an on-going call
and, data to terminate a call. For example, user data can contain
voice, paging, facsimile or other similar data. Portions of this
crosslink received data can be instructional data which are used by
transmit payload satellite 20 (FIG. 1) to modify its operations.
For example, this data can be used by transmit payload satellite 20
(FIG. 1) to determine if any of this data should be stored or
transmitted and on which radio channel the data should be
transmitted.
Transmitted data are sent to communication units 14 (FIG. 1), to
other transmit and receive payload pairs 50 (FIG. 1), and to system
control center 22 (FIG. 1). Transmitted data that is sent to
communication units 14 is identified as downlink transmitted data.
Transmitted data that is sent to other transmit and receive payload
pairs 50 is identified as crosslink transmitted data. Transmitted
data that is sent to system control centers 22 is identified as
downlink telemetry data.
In step 510, the payload data is consumed by transmit payload
satellite 20 (FIG. 1). Payload data can contain but is not limited
to control data, memory data, tracking data, program data, and call
processing data. As an example, portions of the payload data are
used to control the satellite's orientation in space. Other
portions of the payload data are used to control both the downlink
and crosslink antennas.
In step 512, the transmitted data is converted to transmitted
signals by the downlink transmitting device. If downlink
transmitted data is converted, then it is converted into downlink
transmitted signals. If crosslink transmitted data is converted,
then it is converted into crosslink transmitted signals. If
downlink telemetry data is converted, then it is converted into
downlink telemetry signals.
In step 514, the transmitted signals are transmitted. If the
transmitted signals are downlink transmitted signals, then they are
transmitted via the downlink communication channel which is
provided via downlink 18 (FIG. 1) from transmit payload satellite
20 (FIG. 1) to communication units 14 (FIG. 1). If the transmitted
signals are crosslink transmitted signals, they are transmitted via
the long crosslink communication channel which is provided via long
crosslink 28 (FIG. 1) from transmit payload satellite 20 (FIG. 1)
to receive payload satellite 10 (FIG. 1). If the transmitted
signals are downlink telemetry signals, they are transmitted via
the telemetry channel which is provided via telemetry link 26 (FIG.
1) from transmit payload satellite 20 (FIG. 1) to system control
center 22 (FIG. 1). Procedure 500 ends with step 516.
In a preferred embodiment of the present invention, the total
systems approach to a pair of communication satellites are
optimized if the on-board processing on receive payload satellite
10 (FIG. 1) is maximized while the processing load on transmit
payload satellite (FIG. 1) 20 is minimized. This is achieved by
optimizing a receive payload satellite to perform substantially all
of the space-based receiving and processing functions and
substantially none of the associated space-based transmitting
functions; positioning a first number of receive payload satellites
at a first number of first locations in orbits around the earth;
providing at least one uplink communication channel between at
least one of said number of receive payload satellites and at least
one of said plurality of communication units; optimizing a transmit
payload satellite to perform substantially all of the associated
space-based transmitting functions and substantially none of the
space-based receiving and processing functions; positioning a
second number of transmit payload satellites at a second number of
second locations in orbits around the earth; providing at least one
downlink communication channel between at least one of the second
number of transmit payload satellites and at least one of the
plurality of communication units; and establishing at least one
crosslink communication channel between at least one of the first
number of receive payload satellites and at least one of the second
number of transmit payload satellites so that data sent from a
first communication unit is received by a second communication
unit.
Using the apparatus and method of the present invention serves to
balance the thermal and power requirements between the two
satellites. Important to the concept is the optimization of the
major segments of the payload into a receive and process portion
and a high power transmit portion. The characteristics that are
optimized using the transmit and receive payload pair are the
thermal and heat flow aspects of the traveling wave tube amplifiers
(TWTAs) and the complexity versus weight issue in the processor
section. As an example, this could lead to the location of the
on-orbit operations, such as the attitude and orbit control systems
(AOCS) computation, being achieved on receive payload satellite 10.
This could enable the power to be leveled with a dramatic reduction
of computation on transmit payload satellite 20 (FIG. 1) and an
increase in processing requirements on receive payload satellite 10
(FIG. 1). In addition, the major processor tasks (channel resource
assignment, packet routing, and channel allocation) could be left
to receive payload satellite 10 (FIG. 1) with the appropriate
results transmitted to transmit payload satellite 20 (FIG. 1) via
short crosslink 30 (FIG. 1). In addition, all of the
inter-satellite link allocation could be achieved through receive
payload satellite 10. As the feeder links are required, the
allocation could be processed through receive payload satellite 10,
but the transmission would occur through transmit payload satellite
20.
The separation of the receive and processor functions from the
associated transmit functions provides major advantages on the
electromagnetic interference (EMI) and electromagnetic
compatibility (EMC) issues. Separating the functional elements, as
shown in a preferred embodiment of the present invention, minimizes
the EMI and EMC problems because the high power transmitter
operations are physically separated from the sensitive receive
operations.
The crosslink subsystems on both satellites do not require
excessive power, resulting in receive payload satellite 10 (FIG. 1)
being able to use its power to achieve communication services
processing and transmit payload satellite 20 (FIG. 1) being able to
concentrate its power toward sending the message to the user across
significant distances. In addition, those skilled in the art will
recognize that there is only a requirement for large uplink
antennas on receive payload satellite 10 (FIG. 1), a requirement
for large downlink antennas on transmit payload satellite 20 (FIG.
1), and a requirement for small crosslink antennas on both
satellites.
In an alternate embodiment of the present invention, a number of
transmit and receive payload pairs are organized into a
communication system in which each pair covers a different area of
the earth. In this embodiment, the transmit satellite of one pair
could connect to the receive payload satellite of one or more other
pairs via long range crosslinks. These long range crosslinks could
be included in addition to crosslinks 30 (FIG. 1) that connect
transmit payload satellite 20 (FIG. 1) and receive payload
satellite 10 (FIG. 1) in transmit and receive payload pair 50 (FIG.
1).
Additional embodiments of the present invention are envisioned in
which a number of receive payload satellites and different number
of transmit payload satellites are grouped together. For example,
one receive payload satellite could be used in cooperation with
more than one transmit payload satellite to form a communication
group. This could result, for example, where significant
improvements are made in the receive and/or processing operations.
In a second example, one transmit payload satellite could be used
in cooperation with more than one receive payload satellite to form
a different communication group. This could result, for example,
where significant improvements are made in the transmit operations.
These communication groups could also be used in communication
systems in which each group covers a different area of the earth.
In this embodiment, the transmit satellite of one group could
connect to the receive payload satellite of one or more other
groups via long range crosslinks. These long range crosslinks would
be included in addition to crosslinks that connect transmit payload
satellites and receive payload satellites in the communication
groups.
Alternate embodiments of the present invention are applicable to
all orbital types, to include, but not be limited to Low Earth
Orbit (LEO), Medium Earth Orbit (MEO), Geosynchronous Earth Orbit
(GEO), and Highly Elliptical Orbit (HEO). Satellite communication
systems can be established using different numbers of receive
payload satellites 10 (FIG. 1) and transmit payload satellites 20
(FIG. 1) in different orbits. For example, three receive payload
satellites 10 (FIG. 1) could be put into geosynchronous orbits to
control and communicate with more than three transmit payload
satellites 20 (FIG. 1) in one or more non-geosynchronous
orbits.
The large cost of launches and the major issues of frequency and
interference coordination while in orbit provide further incentives
to use a transmit and receive payload pair as a communication
system resource. The cost of placing communications satellites in
orbit is becoming very expensive due to the ever increasing size
and complexity in response to the needs of the customer. A
preferred embodiment of the present invention allows more capacity
to be placed in orbit for less cost and complexity. Optimization of
the communication system is an important result that is achieved by
the method and application of this invention.
Separating the complexity of the receive and processing portion of
the communication service mission from the transmission portion,
which is the energy consuming portion of the communication service
mission, is a technique that provides significant benefits when
applied to a total system. The maturity of the communication
satellite design process enables this optimization to occur,
because the orbits are well understood, the required crosslink
technology is well exercised, and the complexity of the payloads is
being enhanced by faster and larger processors. The separation of
these two subsystems onto separate satellite payloads strengthens
the processing of the communications payload for such issues as
single event upset robust software and sophisticated techniques for
higher data rates.
The present invention has been described above with reference to a
preferred embodiment. However, those skilled in the art will
recognize that changes and modifications can be made in this
preferred embodiment without departing from the scope of the
present invention. For example, while a preferred embodiment has
been described in terms of using specific numbers of payloads and
orbital locations for configuring the transmit and receive pair,
other descriptions or methods can also be employed. Accordingly,
these and other changes and modifications which are obvious to
those skilled in the art are intended to be included within the
scope of the present invention.
* * * * *